Promiscuity of the AlloHLA-A2 Restricted T Cell Repertoire Hampers the Generation of Minor Histocompatibility Antigen-specific Cytotoxic T Cells across HLA Barriers

AbstractHematopoietic system-specific miHAs are ideal targets for adoptive immunotherapy after allogeneic HLA (alloHLA)-matched SCT. Adoptive immunotherapy with cytotoxic T cells targeting hematopoietic system-specific miHAs restricted by alloHLA molecules is an attractive strategy to treat relapsed hematologic malignancies after HLA-mismatched SCT. As a proof of principle, we exploited 2 new strategies to generate alloHLA-A2-restricted miHA-specific T cells from HLA-A2neg donors using a HLA/miHA multimer-guided approach. In one strategy, autologous DCs coated with HLA-A2/miHA complexes were used for in vitro generation of miHA-specific T cells from HLA-A2neg male donors. In the other strategy, miHA-specific T cells were directly isolated from the peripheral blood of HLA-A2neg parous females with HLA-A2pos offspring. Both methods introduced recombinant HLA-A2/miHA complexes as the sole allogeneic target antigen. However, neither method yielded high avidity miHA-specific T cells or prevented the emergence of peptide-dependent promiscuous T cells. The latter T cells resembled miHA-specific T cells so closely with regard to tetramer binding and cytokine production that only extensive testing at a clonal level revealed their nonspecific nature. Therefore, promiscuity of the alloHLA-A2 T cell repertoire of HLA-A2neg individuals hampers in vitro generation of genuine miHA-specific T cells and limits its use for adoptive immunotherapy after HLA-A2 mismatched SCT

The Hematopoietic System–specific Minor Histocompatibility Antigen HA-1 Shows Aberrant Expression in Epithelial Cancer Cells

Allogeneic stem cell transplantation (SCT) can induce curative graft-versus-tumor reactions in patients with hematological malignancies and solid tumors. The graft-versus-tumor reaction after human histocompatibility leukocyte antigen (HLA)-identical SCT is mediated by alloimmune donor T cells specific for polymorphic minor histocompatibility antigens (mHags). Among these, the mHag HA-1 was found to be restricted to the hematopoietic system. Here, we report on the HA-1 ribonucleic acid expression by microdissected carcinoma tissues and by single disseminated tumor cells isolated from patients with various epithelial tumors. The HA-1 peptide is molecularly defined, as it forms an immunogenic peptide ligand with HLA-A2 on the cell membrane of carcinoma cell lines. HA-1–specific cytotoxic T cells lyse epithelial tumor cell lines in vitro, whereas normal epithelial cells are not recognized. Thus, HA-1–specific immunotherapy combined with HLA-identical allogeneic SCT may now be feasible for patients with HA-1+ carcinomas

Minor H Antigen HA-1–specific Regulator and Effector CD8+ T Cells, and HA-1 Microchimerism, in Allograft Tolerance

The role of the hematopoietic lineage-restricted minor histocompatibility (H) antigen HA-1 in renal allograft tolerance was explored. We obtained peripheral blood samples from three recipients of histocompatibility leukocyte antigen (HLA)–matched, HA-1–mismatched renal transplants, one of which had discontinued immunosuppression >30 yr ago while sustaining normal kidney function. Peripheral blood mononuclear cells (PBMCs) were injected into the footpads of severe combined immunodeficiency mice to measure human delayed type hypersensitivity (DTH) responses. All three patients manifested regulated DTH responses to HA-1H peptide. By differential tetramer staining intensities, we observed two distinct minor H antigen HA-1–specific CD8+ T cell subsets. The one that stained dimly had the characteristics of a T regulatory (TR) cell and produced interleukin (IL) 10 and/or transforming growth factor (TGF) β. These HA-1–specific TR cells coexisted with bright tetramer-binding CD8+ T effector (TE) cells. The CD8+ TE cells mediated HA-1–specific DTH and produced interferon-γ. Suppression of these TE functions by TR cells was TGFβ, IL-10, and cytotoxic T lymphocyte–associated antigen 4 dependent. In addition, HA-1 microchimerism was detected in two recipients, primarily in the dendritic cell fraction of the PBMCs. This is the first demonstration of coexisting CD8+ memory TR and TE cells, both specific for the same HA-1 antigen, in the context of renal allograft tolerance

In Situ Detection of HY-Specific T Cells in Acute Graft-versus-Host Disease–Affected Male Skin after Sex-Mismatched Stem Cell Transplantation

HY-specific T cells are presumed to play a role in acute graft-versus-host disease (aGVHD) after female-to-male stem cell transplantation (SCT). However, infiltrates of these T cells in aGVHD-affected tissues have not yet been reported. We evaluated the application of HLA-A2/HY dextramers for the in situ detection of HY-specific T cells in cryopreserved skin biopsy specimens. We applied the HLA-A2/HY dextramers on cryopreserved skin biopsy specimens from seven male HLA-A2+ pediatric patients who underwent stem cell transplantation with confirmed aGVHD involving the skin. The dextramers demonstrated the presence of HY-specific T cells. In skin biopsy specimens of three male recipients of female grafts, 68% to 78% of all skin-infiltrating CD8+ T cells were HY-specific, whereas these cells were absent in biopsy specimens collected from sex-matched patient–donor pairs. Although this study involved a small and heterogeneous patient group, our results strongly support the hypothesis that HY-specific T cells are actively involved in the pathophysiology of aGVHD after sex-mismatched stem cell transplantation